对cron执行的命令有特殊限制吗？ [英] Is there a special restriction on commands executed by cron?

问题描述

我有一个 crontab ，看起来像

0 0 * * * pg_dump DB_NAME > /path/to/dumps/`date +%Y%m%d`.dmp

当我手动运行它，但不是当 cron 运行它。通过日志挖掘，我看到

which works fine when I run it manually, but not when cron runs it. After digging through the logs, I see

Dec 12 00:00:01 localhost crond[17638]: (postgres) CMD (pg_dump DB_NAME > /path/to/dumps/`date +)

百分号，但 man 页面甚至不包含百分比字符，所以我认为他们是好的。

It looks like a problem with percent signs, but the man page doesn't even contain the percent character at all, so I thought they were alright.

推荐答案

您必须用反斜杠转义百分号：

You have to escape percent signs with a backslash:

0 0 * * * pg_dump DB_NAME > /path/to/dumps/`date +\%Y\%m\%d`.dmp

$ b b

man 5 crontab ：

字段（行的其余部分）指定到
的命令是
运行。该行的整个命令部分，直到
换行符或％
字符，将由/ bin / sh或由
中指定的shell执行
SHELL变量crontab文件。
命令中的百分号（％），
除非用反斜杠（\）转义，将被更改为换行符
个字符，第一个％之后的所有数据将被发送到命令
as
标准输入。没有办法将单个命令行
拆分到
多行，就像shell的尾部\。

The ‘‘sixth’’ field (the rest of the line) specifies the command to be run. The entire command portion of the line, up to a newline or % character, will be executed by /bin/sh or by the shell specified in the SHELL variable of the crontab file. Percent-signs (%) in the command, unless escaped with backslash (\), will be changed into newline characters, and all data after the first % will be sent to the command as standard input. There is no way to split a single command line onto multiple lines, like the shell’s trailing "\".

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